Magnification and Penumbra:

image016

  1. Magnification can be varied on an image by changing the location of the source, object, or detector.
  2. Magnification is defined as the ratio of the size of an object in the image to the true size, and, with a little geometry, it can be shown that:

image018, where: 

  1. SID is the source to image distance.
  2. SOD is the source to object distance. 
  1. This leads us to the following ways to increase magnification: 
  1. Move the object closer to the source.
  2. Move the detector farther away. 
  1. Penumbra (P) increases along with magnification, and there is always a balance between penumbral blurring and image resolution.
  2. Image dose also increases with magnification.

 

Scatter Grids:

image020

 

  1. Scatter grids are used in order to reduce the amount of scatter reaching a detector and used for imaging frequently.
  2. Scattered radiation degrades image quality when it is detected because our imaging process relies on linear attenuation.  The grids function to remove the scattered photons from the beam so we do not detect them.
  3. Grids can be either straight or cut to match the divergence of the photons.
  4. In order to remove the attenuation of the bars from the final image, the grid can be rapidly shifted during the image acquisition. This is performed by the Bucky (named after its inventor).

 

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2016-06-09, 21:26
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